San Francisco initially signed Magnuson (6-6, 305) as an undrafted free agent out of Michigan on May 4, 2017. He appeared in eight games with three starts over the past two seasons, including four appearances with one start in 2018.
Update: Magnuson cleared waivers and reverts back to the 49ers' reserve/injured list, according to Nick Wagoner of ESPN. He does not count against the team's 90-man roster.